The present invention relates generally to a tubular implantable prosthesis having knitted textile structure. More particularly, the present invention relates to an endoprosthesis with a knitted textile structure having increased longitudinal stretchability and further having radially restricted enlargement.
An intraluminal prosthesis is a medical device used in the treatment of diseased blood vessels. An intraluminal prosthesis is typically used to repair, replace, or otherwise correct a diseased or damaged blood vessel. An artery or vein may be diseased in a variety of different ways. The prosthesis may therefore be used to prevent or treat a wide variety of defects such as stenosis of the vessel, thrombosis, occlusion or an aneurysm.
One type of intraluminal prosthesis used in the repair of diseases in various body vessels is a stent. A stent is a generally longitudinal tubular device formed of biocompatible material which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body. Endovascular stents have become widely used for the treatment of stenosis, strictures and aneurysms in various blood vessels. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the vessel.
Stents generally include an open flexible configuration. This configuration allows the stent to be inserted through curved vessels. Furthermore, this configuration allows the stent to be configured in a radially compressed state for intraluminal catheter implantation. Once properly positioned adjacent the damaged vessel, the stent is radially expanded so as to support and reinforce the vessel. Radial expansion of the stent may be accomplished by inflation of a balloon attached to the catheter or the stent may be of the self-expanding variety which will radially expand once deployed. Structures which have been used as intraluminal vascular grafts have included coiled stainless steel springs; helically wound coil springs manufactured from a heat-sensitive material; and expanding stainless steel stents formed of stainless steel wire in a zig-zag pattern. Examples of various stent configurations are shown in U.S. Pat. No. 4,503,569 to Dotter; U.S. Pat. No. 4,733,665 to Palmaz; U.S Pat. No. 4,856,561 to Hillstead; U.S. Pat. No. 4,580,568 to Gianturco; U.S. Pat. No. 4,732,152 to Wallsten and U.S. Pat No. 4,886,062 to Wiktor, all of whose contents are incorporated herein by reference.
A graft is another commonly known type of intraluminal prosthesis which is used to repair and replace various body vessels. A graft provides a lumen through which blood may flow. Moreover, a graft is often configured to have porosity to permit the ingrowth of cells for stabilization of an implanted graft while also being generally impermeable to blood to inhibit substantial leakage of blood therethrough. Grafts are typically tubular devices which may be formed of a variety of materials, including textile and non-textile materials.
A stent and a graft may combined into a stent-graft endoprosthesis to combine the features thereof The graft, however, in the stent-graft endoprosthesis should comply with the implantation requirements of the stent which often include collapsing the stent for placement at an implantation site and expansion of the stent for securement thereat. Grafts which cannot easily accommodate the longitudinal and/or radial dimensional changes from a unexpanded or collapsed state to an expanded stent often complicate the implantation of the stent-graft. For instance, some grafts are folded in the collapsed or unexpanded state and must be subsequently be unfolded to accommodate the expanded stent. The unfolding of the graft, however, often complicates the placement of the graft on the stent and the implantation of the stent-graft itself. Alternatively, noncontiguous grafts have been used with expandable stent-grafts. Upon expansion of the stent, however, portions of the noncontiguous graft often separate to accommodate the stent expansion. This separation leaves gaps in the graft structure thereby permitting the leakage of blood through these gaps.
Moreover, an intraluminal device, such as a stent, a graft or a stent-graft, may dilate over time after implantation within a bodily lumen. The dilation of the implanted intraluminal device is a radial enlargement of the device resulting from pulsating stresses or pressures present within the bodily lumen. The action of the pulsating stresses or pressures often fatigue the structure of the device resulting in radial expansion and possibly longitudinal foreshortening.
A variety of mechanical means have been used to attempt to limit device dilation. For example, U.S. Pat. No. 5,843,158 to Lenker et al. describes the use of generally inelastic frame rings circumferentially disposed along a radially contractible stent-graft. The frames are described as limiting the radial expansion. Such frames, however, must be integral to the stent and complicate the stent-graft geometry.
U.S. Pat. No. 5,843,158 to Lenker et al. further describes mechanical means for limiting radial expansion of a graft in a stent-graft. In one alternative, the stent graft includes an internal liner. The internal liner is described as an inelastic material and is folded within the stent graft. Upon radial expansion of stent-graft, the internal liner is described as further limiting the radial expansion of the stent-graft. Furthermore, a graft containing circumferential composite yarns is described as yet another alternative for limiting radial expansion. The composite yarns are described as having inexpansible yarns counter wound or braided over an elastic core yarn. The inexpansive yarns are described as limiting radial expansion of graft. These attempts to limit radial expansion of a stent-graft, however, result in complicated the stent-graft designs that have either additional liners or complex composite yarn designs.
Thus, there is a need for a graft that compliments the implantation of an expandable stent of a stent-graft endoprosthesis and limits dilation without the disadvantages of the prior art. In particular, there is need for a graft that is securably attached to the stent in both the expanded and unexpanded state which limits without complicating the mechanical dynamics of the stent or the graft.
The present invention provides an implantable tubular prosthesis having a radially expandable tubular stent structure having a first diameter and capable of longitudinal expansion or contraction to achieve a second diameter which is different from the first diameter and a tubular knitted tubular graft circumferentially disposed and securably attached to the stent. The graft has a pattern of interlaced wale and course yarns in a warp knit pattern to permit longitudinal expansion or contraction of the graft substantially consistent with the longitudinal expansion or contraction of the stent.
The prosthesis of the present invention is capable of longitudinal expansion from 50 to 200 percent by length from a quiescent state. Alternatively, the prosthesis of the present invention is capable of 50 to 200 percent longitudinal contraction by length to achieve a substantially quiescent state from an unexpanded state. Furthermore, the textile graft of the present invention is substantially fluid-tight in its quiescent state.
To achieve such a degree of longitudinal expansion or contraction the textile graft includes a single layer, warp knit pattern having a set yarns diagonally shifted over two or more yarns before forming a loop between engaging yarns. The knit pattern is generally described as a warp knit pattern with at least a two needle underlap. Such patterns depart a high degree of flexibility and stretchability to the textile graft of the present invention. Moreover, such patterns substantially inhibits radial expansion of the textile graft beyond a desired diameter to limit dilation of the graft.
In one aspect of the present invention an implantable tubular prosthesis is provided which is capable of longitudinal expansion from a quiescent state to an elongated state including a radially contractible and longitudinally expandable tubular stent having a quiescent diameter and quiescent length capable of longitudinal expansion to the elongated state having an elongated length and a contracted diameter, wherein the elongated length is greater than the quiescent length and the contracted diameter is smaller than the quiescent diameter. The prosthesis further includes a tubular knitted tubular graft circumferentially disposed and securably attached to the stent in the quiescent state. The graft has a single layer of yarns interlaced into stitches in a knit pattern capable of resilient longitudinal elongation and resilient radial contraction of the graft to the elongated state. The graft has from 400 to 1,000 stitches per square centimeter to provide compliancy in the quiescent state. The knit pattern is a warp knitted pattern of yarns forming a textile layer having an interior surface and an exterior surface, wherein interior yarns predominate the interior surface and form loops in the longitudinal direction of the prosthesis, and exterior yarns predominate the exterior surface and are diagonally shifted over two or more of the interior yarns in an alternating pattern along a width of the prosthesis before engaging an interior yarn.
In another aspect of the present invention, the prosthesis includes a longitudinally expandable stent and an expandable warp knitted graft having a single layer of yarns to define a single layered graft wall having a thickness from 0.3 to 0.4 millimeters. The yarns are interlaced into stitches in a knit pattern capable of resilient longitudinal elongation and resilient radial contraction of the graft to an elongated state. The graft has greater than 350 stitches per square centimeter to provide compliancy in its quiescent state. The knit pattern is a warp knitted pattern of yarns forming a textile layer having an interior surface and an exterior surface, wherein interior yarns predominate the interior surface and form loops in the longitudinal direction of said prosthesis, and exterior yarns predominate the exterior surface and are diagonally shifted over two or more of the interior yarns in an alternating pattern along a width of the prosthesis before engaging an interior yarn.
In still another aspect of the present invention, the prosthesis includes a longitudinally expandable stent and an expandable warp knitted graft having a single layer of yarns to define a single layered graft wall. The yarns are interlaced into stitches in a knit pattern capable of resilient longitudinal elongation and resilient radial contraction of the graft to an elongated state wherein the elongated length is from 50 to 200 percent by length greater than the quiescent length. The graft has greater than 350 stitches per square centimeter to provide compliancy in its quiescent state. The knit pattern is a warp knitted pattern of yarns forming a textile layer having an interior surface and an exterior surface, wherein interior yarns predominate the interior surface and form loops in the longitudinal direction of said prosthesis, and exterior yarns predominate the exterior surface and are diagonally shifted over two or more of the interior yarns in an alternating pattern along a width of the prosthesis before engaging an interior yarn.
In a further aspect of the present invention, the prosthesis includes a longitudinally expandable stent and an expandable warp knitted graft having a single layer of yarns to define a single layered graft wall. The yarns are interlaced into stitches in a knit pattern capable of resilient longitudinal elongation and resilient radial contraction of the graft to an elongated state. The graft has greater than 350 stitches per square centimeter to provide compliancy in its quiescent state. The knit pattern is a warp knitted pattern of yarns forming a textile layer having an interior surface and an exterior surface, wherein interior yarns predominate the interior surface and form loops in the longitudinal direction of said prosthesis, and exterior yarns predominate the exterior surface and are diagonally shifted over two or more of the interior yarns in an alternating pattern along a width of the prosthesis before engaging an interior yarn. The stent and the graft are resiliently deformable between the quiescent and the elongated states and the graft is capable of non-bulging contraction from the elongated state to the quiescent state to circumferentially abut the stent.
In other aspects of the present invention, a non-textile, desirably ePTFE, layer is provided with the endoprosthesis of the present invention. Furthermore, an implantable medical fabric is provided. The medical fabric is a knitted textile with a high degree of stretchability because of the warp knit pattern with at least a two needle underlap used to form the fabric. Moreover, a method for warp knitting a tubular graft with a warp knit pattern with at least a two needle underlap.